The present invention relates to an integrated system for finishing the cylindrical interior of a workpiece such as a hydraulic cylinder.
A hydraulic or pneumatic cylinder is typically roughly formed in a steel mill by drawing a steel blank over a mandrel. As the steel is drawn over the mandrel, particulate matter often becomes embedded in the interior surfaces of the cylinder, and imperfections in the mandrel form corresponding imperfections on the interior of the cylinder. As a result, the interior surfaces of the cylinder must be finished so that the cylinder is usable for hydraulic or pneumatic applications.
Perhaps the most common technique for finishing the interior surface of the cylinder is to hone the cylinder until smooth. This technique for finishing the interior of the cylinder is relatively inefficient because a hone is primarily designed to remove relatively small amounts of material so that the surface becomes quite smooth.
A relatively large amount of time and effort is required to remove the rather substantial imperfections initially present in the cylinder blank. A far more efficient technique would be to initially cut the interior of the cylinder to its approximate final dimensions, before smoothing the interior surface with a honing tool.
A technique has recently been developed for finishing the interior surfaces of a cylinder on a single machine. A skiving and roller burnishing tool, such as those shown in U.S. Pat. Nos. 3,795,957 and 4,133,089, finishes the interior of the cylinder in a single step. The skiving portion of the tool machines the interior of the cylinder, and the roller burnishing portion smoothes out the imperfections of the machining.
This latter technique has the advantage of finishing the interior of the cylinder in a single operation, but has been found to have certain drawbacks. The roller burnishing forms a surface on the interior of the cylinder which is actually too smooth in most applications. The slight cross hatching provided by a honing tool in the conventional system is useful to allow oil to permeate the sidewalls of the cylinder, and the smooth walls formed by roller burnishing cannot provide this feature. As a result, the oil does not reach the seals, causing them to wear prematurely. In addition, roller burnishing compresses the material, which can cause laminations subject to potential delamination. Also, the combined skiving and roller burnishing tool required is relatively expensive and subject to failure.